1. Field of the Invention
The present invention relates to an illumination apparatus and a projection-type image display apparatus, which utilize fourth color component light in addition to red component light, green component light and blue component light.
2. Description of the Related Art
Conventionally, a projection-type image display apparatus has been known, which provided with three light valves corresponding to light of three colors, a cross dichroic cube that combines light beams emitted from three light valves and a projection mean that projects light combined by the cross dichroic cube.
Herein, the cross dichroic cube has three light incident surfaces on which light enter and one light emitting surface from which light is emitted. Accordingly, in the case of using three colors of light to be incident on the cross dichroic cube, it suffices that the projection-type image display apparatus has one cross dichroic cube.
On the other hand, for the purpose of improving color reproduction capability and luminance, there has been proposed a projection-type image display apparatus using four or more colors of light. By using, for example, orange, yellow, or cyan light in addition to three colors of red, green, and blue light, such a projection-type image display apparatus is intended to improve color reproduction capability and luminance (for instance, see Japanese Patent Publication No. 2002-287247 (Claims 1 and 4, FIG. 1, and the like)).
When light beams of four colors or more are utilized in the projection-type image display apparatus, light beams of four colors or more cannot be combined by one cross dichroic cube. For this reason, the projection-type image display apparatus should be provided with a plurality of dichroic cubes (or cross dichroic cubes).
For example, when a combination of light beams of four different colors is needed, the projection-type image display apparatus obtains two combined light beams in each of which light beams of two different colors are combined, and further combines the two combined light beams to obtain a combined light beam of four different colors. In addition, the projection-type image display apparatus may obtain a combined light beam in which light beams of three different colors are combined and combine the obtained light beam with one color light beam to obtain a combined light beam of four different colors. Moreover, the projection-type image display apparatus may obtain a combined light beam in which light beams of two different colors are combined and combine the obtained light beam with color light beams of two different colors to obtain a combined light beam of four different colors.
Here, an optical path length from each of the light valves corresponding to four or more colors to the projection mean should be the same. Moreover, there is need to provide a plurality of dichroic cubes (or cross dichroic cubes) between the light valves and the projection mean. Accordingly, the back focus of the projection mean becomes longer.
As a result, a projection mean used in a projection-type image display apparatus using light of three colors cannot be used for the one using light of four or more colors, leading to an increase in manufacturing cost of the projection-type image display apparatus as a whole.